Carburetor construction



Sept. 24, 1957 w. o. MANNING, JR

CARBURETOR CONSTRUCTION Filed Sept. 7, 1954 h mm MM VA mM 0. M M M H/ wY I B I 1 W I I United States Patent Ofitice 2,807,449 Patented Sept.24, 1957 CARBURETOR CONSTRUCTION William O. Manning, In, Detroit, Mich.,assignor to Holley Carburetor Company, Detroit, Mich., a corporation ofMichigan Application September 7, 1954, Serial No. 454,507

2 Claims. (Cl. 26,141)

This invention relates generally to carburetors of the type employed forfeeding fuel mixture to internal combustion engines and refers moreparticularly to an improved idling or low speed jet system forcarburetors.

Internal combustion engines employed to propel Vehicles are usuallyprovided with a carburetor of the down draft type having an idling jetcommunicating with the fuel mixture supply passage at the down streamside of the throttle valve and also communicating with the upper end ofan idling tube to receive fuel from the latter. The lower end of theidling tube ordinarily extends into a fuel well which is connected by amain metering jet to a fuel supply or float bowl of the carburetor.

The primary function of the idling system is to assure delivery of anample supply of fuel mixture to the engine when the throttle valve isclosed or substantially closed. However, in many installations the fuelsupply bowl occupies such a position that rapid deceleration of thevehicle resulting from closure of the throttle valve while the vehicleis moving forward, causes the supply of fuel in the bowl to surge in adirection away from the main metering jet and this surging action has atendency to effect a reverse flow of fuel through the main metering jetwith a corresponding lowering of the fuel level in the well whichcommunicates with the lower end of the idling tube. This reverse flow offuel through the main metering jet produces a force which opposes theintake manifold vacuum tending to draw fuel through the idling jet andin severe cases this force becomes sufiicient to cause stalling of theengine.

With the above in view, it is an object of this invention to overcomethe tendency for the vehicle to stall upon deceleration by providing theidling tube with an air bleed situated to interrupt the fuel passageextending from the idling discharge jet to the fuel Well at the bottomof the idling tube. As a result, the force tending to produce reverseflow upon deceleration is reduced to a negligible quantity in theportion of the fuel passage between the idling discharge jet and pointof interruption.

It is another object of this invention to locate the air bleed asclosely as possible to the normal level of the fuel in the wellcommunicating with the lower end of the idling tube so that the maximumvolume of fuel is available in the portion of the passage extending fromthe idling discharge jet to the air bleed. Hence, ample supply of fuelis available at the idling jet to maintain operation of the engineduring the relatively short surging period of the fuel in the supplybowl.

It is a further object of this invention to locate and so proportion thesize of the air bleed in the idling tube that it serves the additionalpurpose of enrichening the fuel mixture in the idling fuel passage atthe time the main fuel nozzle begins to flow. Thus, the meteringcharacteristics of the carburetor are improved and superior performanceis assured regardless of changing conditions.

The foregoing as well as other objects will be made more apparent asthis description proceeds especially when considered in connection withthe accompanying drawing, wherein:

Figure 1 is a semi-diagrammatic sectional view of a carburetor of thedown draft type and embodying the features of this invention; and

Figure 2 is an enlarged sectional view of a part of the carburetor shownin Figure 1. V v

The carburetor selected for the purpose of illustration is of the downdraft type having a housing 10 formed to provide a vertically extendingpassage 11 and a float bowl 12. The lower end of the passage 11communicates with an intake manifold of an internal combustion engine(not shown) and the upper end of the passage 11 communicates with theatmosphere or an air supply. A venturi 13 is provided in the passage 11intermediate the ends thereof and a throttle valve 14 is supported inthe passage 11 at the downstream side of the venturi 13. A choke or aircontrol valve 15 is suitably mounted in the passage 11 at the upstreamside of the venturi 13 for regulating the amount of air drawn into thesystem to facilitate starting the engine when the latter is cold.

The float bowl 12 communicates with the passage 11 above the choke valve15 and is adapted to contain a supply of fuel determined by a float 16.Fuel is supplied to the bowl 12 through a passage 17 and the quantity offuel admitted to the bowl 12 is regulated by a valve 18 operativelyconnected to the float 16 for actuation by the latter. A main meteringjet or restriction 19 establishes communication between the bowl 12 anda well 20 in a manner such that the level of the fuel in the well isnormally the same as the level of the fuel in the bowl 12.

The well 20 communicates at a point above the normal level of the fueltherein with a main fuel discharge nozzle 21 positioned in the throat orrestricted area of the venturi 13 to discharge fuel in a downwarddirection toward the throttle valve 14. The arrangement is such thatwhen the throttle valve 14 is opened substantially, considerable suctionis produced in the Venturi throat and fuel is drawn upwardly from thewell 20 through the main nozzle 21.

When the throttle valve 14 is closed or practically closed, the suctionat the Venturi throat drops considerably and very little, if any, fuelis drawn through the main nozzle 21. In order to assure the supply offuel required to maintain operation of the engine at closed orpractically closed throttle conditions, a low speed jet or idling nozzle22 is provided at the downstream side of the throttle valve 14 where thesuction is relatively high under these conditions. A needle valve 23 isthreadably supported on the housing 10 in a position to regulate theflow'through the idling jet 22 in accordance with conventional practice.

Fuel is supplied to the idling-jet 22 by a passage.24

formed in one wall of the housing Ill and extending upwardly from theidling jet 22 to a point above the venturi 13. The upper end of thepassage 24 extends forwardly across the passage 11 and communicates withthe well 20 at a point spaced above the point of communication of themain fuel discharge nozzle 21 with the well 24 Fuel is admitted to theupper end of the passage 24 from the Well 20 through an idling tube 25having a head 26 at the upper end threadably mounted in the well 20above the point of communication between the passage 24 and well 20. Thelower end of the tube 25 is reduced in diameter and projects downwardlyto a point below the normal level of the fuel in the well 28. Thevertical passage through the tube 25 is indicated by the numeral 27 andterminates short of the head 26. The head 26 has an annular groove 23 inregistration with the intake end of the passage 24 and a bore 29 isformed in the side of the head to connect the groove 28 to the passage27.

flowing .upwardly through the tube 25 during operation of the idling jet22.

As stated above, when thethrottle valve 14 is closed or practicallyclosed, the manifold suction at the throat of 1 the venturi 13 or' atthe main discharge jet 21. drops 1 substantially so that very little, if"any, fuel is'drawn from the well 20 through the main discharge jet 21.However, the suction in the passage .11 at the downstream side of thethrottle valve 14 is increased to such an extent that fuel is drawn fromthe well through the idling tube 25 and passage 24 to the idlingdischarge jet 22.. Also, a small quantity of air is drawn into the fuelstream through the bleed 30 and the resulting emulsion is dischargedinto the passage 11 through the jet 22. Supplemental jets 31 may be, andpreferably are provided at the upstream side of the jet 2 2. Thesupplemental jets 31 function when the throttle valve 14 is practicallyclosed to admit additional airinto the passage 24 and when the throttlevalve 14 is opened farther to admit additional fuel mixture into thepassage 11. By reason of the above arrangement, the socallcd fiatspot-is eliminated in the mixture-ratio curve within the range of speedswhere the delivery was taken over from the idling nozzle 22 by the mainnozzle 21.

In the present instance, the carburetor is installed With the bowl 12 insuch a position that when the vehicle is rapidly decelerated, the fuelcontained in the bowl 12 and well 26 surges forwardly or in a directionto cause reverse flow of fuel in the main metering jet 19. However, theforce produced by such reverse fiow through the jet 19 is dissipated ormaterially reduced at the air bleed orifice 30 in the idling tube 25 sothat it has little or no effect on the fuel mixture contained in thelength of the passage extending from the idling jet 22 to the air bleedorifice 30. Hence, any opposition that this force produces on normalflow of the fuel mixture through the idling jet 22 by the manifoldvacuum is negligible. Moreover, since the air bleed 30 is locatedinclose proximity to the normal level of the fuel in the well 20, amplefuel mixture is available beyond the bleed orifice 30 to assuremaintaining operation of the engine during the relatively short timerequired for the fuel to return to its normal level in both the bowl 12and well 20.

The location of the air bleed 30 in the side of the idling tube 25 abovethe normal level of the fuel in the well 20 also renders it possible toimprove the metering characteristics of the carburetor. In thisconnection, it will be understood that when the throttle valve 14 ismoved from its idling position toward its open position, the manifoldvacuum at the restriction of the venturi is greatly increased with theresult that the suction created at the main discharge jet 21 becomessufficient to draw, fuel upwardly from the well 20 into the venturi. Inother words, the level of the fuel in the well 20 is raised to the pointof communication of the main discharge jet 21 with the well 20 by theincreased suctionresulting from opening 4 the throttle'valve 14. Asshown in Figure 1 of the drawing, the air bleed 30 in the idling tube 25is positioned slightly above the point of communication of the maindischarge jet 21 with the well 20. Actually, the air bleed 3% is locatedin such a position with respect to the point of communication of themain discharge jet 21 with the well 26 that it bleeds the idling tube 25with an emulsion of fuel and air at the time the main nozzle 21 startsits flow. In other words, the fuel mixture in the idling system isenriched at the time the main fuel discharge nozzle 21 becomes operativeand this is desirable in that it assures more satisfactory distributionof fuel to the engine when the throttle valve 14 is opened. It will alsobe understood that the size of the bleed orifice 30 may be varied toobtain the most desirable metering characteristics for a given set ofconditions.

What i claim as my invention is:

1. A carburetor for an internal combustion engine of an automotivevehicle comprising a body having an induction passage for fuel mixture,a float chamber in said body, a vertically elongated well in said body,a fuel metering jet connecting the chamber and well adjacent the bottomof the well, a main nozzle in said induction passage, a throttle valvein said induction passage downstream from said main nozzle, an idle tubein said well defining an annular chamber between the inner surface ofsaid well and the outer surface of said tube, said tube having an intakeopening adjacent its lower end, a main supply passage connecting saidmain nozzle to said annular chamber adjacent the top of said well, anidle nozzle in the side of said induction passage adjacent saidthrottle, an elongated idle passage connecting said idle nozzle to thetop of said tube, means mounting said carburetor in position such thatdeceleration resulting from throttle valve closure while the vehicle ismoving in a forward direction displaces fuel in said float chamber in adirection to draw fuel through said metering jet from the bottom of saidwell, and a bleed orifice in the side of said tube closely adjacent thejuncture between said well and said main supply passage and forming adirect connection between said annular chamber and the interior ofsaididle tube.

2. A carburetor as defined in claim 1 in which said bleed orifice isjust above the juncture between said ,well

F and said main supply passage.

References Cited in the file of this patent UNITED STATES PATENTS1,631,716 Bavcry June 7, 1927 1,821,012 Guthrie Sept. 1, 1931 1,881,256Ball et al. Oct. 4, 1932 2,419,956 Kuzelka May 6, 1947 2,615,696 WinklerOct. 28, 1952 2,628,826 Worden Feb. 17, 1953 2,656,166 Foster Oct. 20,1953 2,676,004 Bimberg Apr. 20, 1954 2,689,115 Olson Sept. 14, 1954

